1. Field of the Invention
The present invention relates to the field of single in-line memory module (SIMM) connectors, and in particular to an improved memory module latching mechanism for a SIMM connector. More generally, the invention relates to latching mechanisms for removably attaching circuit cards or "daughter" boards to a mother board or other printed circuit device.
2. Description of Related Art
The SIMM connector is a connector which permits edgewise mounting of a memory chip circuit module onto a printed circuit board, and provides an electrical connection between contact surfaces of the "daughter" or "baby" board which carries the memory chips and contact areas of the printed circuit board, or "mother" board. Since their introduction only a few years ago, SIMM connectors have attained widespread acceptance for use in computers of all types, including personal computers, workstations, and mainframes. Reasons for their popularity include the fact that the edgewise mounting arrangement made possible by the SIMM connector sharply reduces the space occupied by a memory module on the mother board. Also, because of the releasable latch mechanism developed for the SIMM connector, SIMM technology permits field replacement of not only the connectors themselves, but also of individual memory modules. This later feature has made it possible to easily upgrade to higher density RAMs as they became available, the circuitry changes being made on the module rather than on the mother board. In addition, although at present generally used for memory chips, SIMM technology can also be used to facilitate installation and replacement of custom manufactured integrated circuit chips, a possibility that offers virtually unlimited opportunity for continued expansion of the technology in the near future.
Several versions of the SIMM connector are currently being manufactured, but each includes a plurality of contacts which extend from a first mating surface of the connector to a second mating surface. The contacts have posts which extend from the first mating surface and are arranged to electrically engage the contact areas of the mother board when the connector is plugged into or otherwise secured thereto. The daughter board is inserted into a groove in the second mating surface of the connector and rotated to its operating position. As this rotation occurs, contact projections of the contacts engage the contact surfaces of the daughter board. In order for this electrical engagement to be maintained, latch arms are provided to cooperate and securely but releasably maintain the daughter board in the operational position.
Examples of this type of electrical connector are described in U.S. Pat. Nos. 4,737,120 and 4,850,892. In each example, the latch members are provided at the ends of the connector, and are integrally molded with the housing. This configuration of the latch members provides the latch members with the resilience characteristics required in order to allow the latch members to cooperate with the daughter board or SIMM to maintain the daughter board in electrical engagement with the terminals of the connector.
Although representing a clear improvement over other board mounting arrangements, however, several problems are associated with the latch configuration described above. Because the latch members are molded from plastic material, and because the resilience characteristics of plastic are less than those of metal, conventional plastic latches are likely to take a permanent seat, particularly when the connector is use dover many SIMM insertion and removal cycles. This likelihood is increased due to that the fact the latch members must have a relatively thin width when molded. This requirement reduces the durability of the latch members and, consequently, if the electrical connector is to be used over many cycles, the risk of failure of the electrical connector is great.
The problem is exacerbated by the fact that the daughter boards often vary in size while still falling within tolerance limits for the connector. Thus it is possible that a relatively large board will be inserted into the groove or slots in the second mating surface, and then be followed by a relatively small board. The insertion of the large board into the groove can cause the plastic latch to take a permanent set or weaken, so that when the smaller board is inserted, the latch will not be as effective in maintaining the board in the slot, resulting in an ineffective connector.
One proposed solution to these problems is disclosed in U.S. Pat. No. 4,986,765. As described in this patent, the proposed solution is to construct the latch metal as a discrete member which replaces the prior molded-in latch and is mounted in a latch-receiving recess provided in the connector. The latch includes a resilient section for latching the SIMM or daughter board and a mounting section which extends from the base of the resilient section and is dimensioned to extend through the recess and be received in an aperture of the mother board.
In order to provide a stable attachment of the latch to the SIMM connector and mother board, since the metal latch is not integrally molded in, a relatively complex latch mounting arrangement is used. The latching mounting structure includes a U-shaped portion, one arm of which engages a wall of the recess in a stressed condition to secure the latch in position. In addition to requiring a special mounting section, the metal latch design requires separate shaping of the latching projection which permits the board to be rotated into place and subsequently secured. Thus, the all metal design, while solving the problems of weakness and lack of resilience inherent in the molded-in all-plastic design, results in greatly increased complexity and manufacturing costs.
In overcoming the problems of the all-plastic design, the metal latch design therefore loses the manufacturing and cost advantages provided by forming the SIMM connector, including the latch arms, in a single mold, and of necessity adds a complex mounting section and latching projection section which are sources of both manufacturing difficulties and potential failure during use.
In view of the above problems, it would be desirable to provide a latch for a SIMM-type connector which is simpler in design than the metal latch, and yet which is more resilient and less subject to setting during repeated use cycles than is the all-plastic design.